Managed Pressure Drilling Saves Multimillion Dollar Well from Abandonment; Enabled Operator to Drill and Isolate Section to Target Depth in a Challenging Plastic Salt Formation

Abstract

The Northern Potwar Plateau of Pakistan is known for its severe geological features. Many wells have been drilled in the region, but geological correlations in neighboring fields have proven to be challenging. Excessive tectonic activity and faults have resulted in formation repetitions, abnormal in-situ stresses, and variable formation pore and fracture pressures.

One such field in the region is MDK field, where the operator was in the process of drilling a second well. Drilling of the 8 ½-in. hole section was in progress at 11,004 ft. (3,354 m) when the Bahadur Khel Salt formation was encountered. Upon drilling further into the formation, the operator encountered severe hole stability issues coupled with lost circulation. While in the salt formation, whenever circulation was stopped and annular pressure losses were eliminated, the drill string would become stuck. Upon resuming circulation, the pumping pressure would rise abruptly. The formation was highly stressed and was exhibiting a creeping behavior. Any reduction in the bottom hole pressure (BHP) would cause the formation to creep into the wellbore.

The operator spent a month attempting to drill through the highly stressed plastic salt formation, without success. The oil-based mud system was already weighted up to its maximum, and no other conventional means existed of controlling the creeping salt. The operating company had already spent ~USD 19 million dollars on the well, and was considering abandoning it after a nearby well in the same formation had been abandoned despite four unsuccessful sidetracks.

Maintaining a constant bottom hole pressure (CBHP) across the formation at all times was the only way to stabilize the salt formation and lost circulation treatment. Only managed pressure drilling (MPD) could achieve the application of CBHP. An MPD system would enable the operator to compensate for the lack of BHP by applying surface backpressure, thereby maintaining the target pressure across the formation at all times. With the help of the MPD system, the operator also sought to calculate the formation creep rate, so as to evaluate a time window for running in and out of the hole.

Besides drilling, the operator also intended to isolate the challenging section with a liner. With proper planning, the MPD system could help to achieve this objective.

A full MPD system was deployed to the wellsite and drilling resumed with a CBHP in dynamic and static periods. By CBHP MPD, the operator was able to tag bottom. Drilling and underreaming of the 8 ½-in. hole section resumed and continued until reaching the target depth of 14,745 ft. (4,494 m). After drilling, the 7-in. liner was set and cemented to the target depth using MPD.

Applying CBHP MPD enabled the operator to drill through 3,832 ft. (1,168 m) of the hole section and save the well from abandonment. This paper studies the design, execution, and lessons learned when applying MPD on the subject well.